This invention relates to a method and apparatus for dry offset intaglio printing in which a dry offset printing and an intaglio printing are effected continuously with a single machine.
In the dry offset printing, an image formed on the surface of a plate cylinder is transferred onto a blanket cylinder and then the image is transferred onto a paper sheet between the blanket cylinder and an impression cylinder, whereas in the intaglio printing an image formed on the intaglio plate on an intaglio cylinder is transferred onto a paper sheet between the intaglio cylinder and an impression cylinder.
Since impression cylinders of the same type and designed for the same purpose are used for both the dry offset printing and the intaglio printing, a combination type printing press capable of continuously effecting the dry offset printing and the intaglio printing with a single machine by utilizing a single impression cylinder for both types of printing has been developed. Such a machine is mainly used for printing such precise multicolor printed matter as bank notes and valuable securities.
FIG. 1 is a side view of a prior art dry offset intaglio printing press of the type described above. The printing press 1 shown in FIG. 1 comprises a sheet feed device 2, printing machine 3 and a delivery apparatus 4. The sheet feed device 2 includes a stack board 6 which supports stacked sheets 5 and is raised automatically, a sucker and a feed roller, not shown, which mounts sheets 5, one after one, onto a feed board 7. The printing machine 3 comprises an impression cylinder 8 wrapped with a blanket, not shown. The impression cylinder 8 is rotated in the direction of arrow A and a sheet 5 supplied from the feed board 7 through a swinging member 9 and paper transfer cylinders 10 and 11 is gripped by grippers (not shown) provided on the outer periphery of the impression cylinder 8 and wrapped thereabout. A blanket cylinder 12 having the same diameter as the impression cylinder 8, wrapped with a blanket, not shown, and rotated in the direction of arrow B is positioned on the right lower position of the impression cylinder 8. The periphery of the blanket cylinder 12 is maintained in contact with the impression cylinder. Four plate cylinders 13 respectively mounted with plates for dry offset printing and having a diameter of about 1/4 that of the blanket cylinder 12 are provided on the righthand side of the blanket cylinder 12 in contact therewith. Ink supply device generally shown by a reference numeral 14 is provided to supply ink onto the plate surfaces of the plate cylinders 13. The ink supply device 14 is constituted by four ink fountain 15 storing inks of different colors, inking rollers, not shown, facing respective plate surfaces and groups of rollers, not shown, disposed between the ink fountains 15 and the inking rollers. On the lower left side (that is the side of the sheet delivery apparatus) of the impression cylinder 8 is disposed an intaglio cylinder 16. This cylinder is rotated in the direction of arrow C and has the same diameter as the impression cylinder 8. The intaglio cylinder 16 is mounted with four intaglio plates each having an intaglio image at an equal peripheral spacing. The intaglio cylinder 16 is also maintained in contact with the impression cylinder 8. On the side of the sheet delivery apparatus 4 are disposed three pattern rollers 17 each having a diameter of about 1/4 of the intaglio cylinder 16. The pattern rollers 17 are also maintained in contact with the intaglio cylinder 16. An inking device 18 is provided for supplying ink to the intaglio plates of the intaglio cylinder 16 via the pattern rollers 17. Also the inking device 18 is constituted by three ink fountains 19 storing inks of different colors, and groups of rollers, not shown. A wiping device 20 is provided including a liquid tank 21 containing a detergent and a wiping roller 22 rotating in the detergent. The wiping device 20 is constructed to wipe off surplus ink adhered to the intaglio cylinder. The sheet delivery apparatus 4 is provided with a pair (left and right) of endless chains 26 each passing about a sprocket wheel 23 mounted on the shaft of a sheet receiving cylinder in contact with the impression cylinder 8 and about a sprocket wheel 25 at the front end of a frame 24 of the sheet delivery apparatus 4. A sheet stacking board 27 is provided beneath the front end of the endless chains 26.
In the printing press 1 described above, the sheets 5 sent onto the feed board 7 one after another from the stack board 6 are sequentially wrapped and transferred about the impression cylinder 8 via the swinging member 9 and the sheet transfer cylinders 10 and 11. Inks of different colors are supplied to the respective plate cylinders 13 from the ink fountains, and the images formed by the inks are transferred onto the blanket cylinder 12 as four dry offset images of four colors. Inks of three colors from the ink fountains 19 are also applied to recessed image forming portions and flat non-image portions of the intaglio plates mounted on the intaglio cylinders 16. The inks on the non-image portions are wiped off by the wiping roller 22 so that intaglio images of three colors whose inks are rubbed into the intaglio plates are left. In this manner, the four dry offset images formed on the blanket cylinder 12 are transferred onto the sheet 5 carried by the impression cylinder 8 and then the four intaglio images formed on the intaglio cylinder 16 are transferred onto the sheet 5. The sheet 5 thus printed is conveyed by the sheet delivery chains 26 to be stacked on the stack board 27.
Since the dry offset intaglio printing press having a construction described above is used to print such printed matter as paper monies and valuable securities for the purpose of preventing counterfeit, a highly precise registering accuracy is desired. Especially, a high registering accuracy between the dry offset printing and the intaglio printing is desired. To obtain an extremely high registering accuracy in the prior art, the difference in the printing pressure between the intaglio printing and the dry offset printing presented a problem. More particularly, in the intaglio printing an extremely large printing pressure has been desired for the purpose of transferring inks rubbed into the recesses of the intaglio plate onto the sheet, whereas in the dry offset printing a relatively small printing pressure is sufficient. Thus, when these two types of printing are made with a common impression cylinder 8, the large printing pressure applied during the intaglio printing causes deflection of the shaft of the impression cylinder 8 as well as bearing clearance with the result that the displacement of the axis of the impression cylinder 8 causes a phase difference between the impression cylinder 8 and the blanket cylinder 12, thereby greatly impairing the registering accuracy of the dry offset printing. When the intaglio printing is made under a high printing pressure between the impression cylinder 8 and the intaglio cylinder 16 immediately after the dry offset printing in which the printing pressure between the impression cylinder 8 and the blanket cylinder 12 is small, so that the dimension of the sheet does not vary appreciably, the dimension of the sheet 5 would vary substantially, thus resulting in non-registration of the dry offset printing and the intaglio printing.
For this reason, as shown in FIG. 1, the angle between a line interconnecting the axes of the impression cylinder 8 and the blanket cylinder 12 and a line interconnecting the axes of the impression cylinder 8 and the intaglio cylinder 16 is made to be 90.degree. so as to prevent the displacement of the axis of the impression cylinder caused by a large printing pressure at the time of the intaglio printing from causing the variation in the dry offset printing pressure. Even with this measure, the displacement of the axis of the impression cylinder 8 caused by the printing pressure at the time of the intaglio printing acts in the direction of rotation of the blanket cylinder 12 so that a satisfactory result can not always be expected. As a countermeasure for the variation of the sheet size, a method has been tried in which the dimension variation of the sheet caused by the pressure at the time of the intaglio printing is converted into data representing the real value of the elongation based on the actual printing result and in which, at the time of manufacturing the plates, an elongation percentage on the basis of the above described data is used as a correction value between the intaglio plate and the dry offset plate. But the data thus obtained differs from the actual printing result in many cases, thus failing to obtain satisfactory results.